The invention relates to an envelope-generating apparatus which is incorporated in an electronic musical instrument and adapted to generate envelope signals for musical tones, and more in particular, the invention relates to a system wherein quickly weakened or attenuated are some of the musical tones which are being generated but need not or should not continue because musical timbre is changed during a musical performance, or because there is no channel which is free to be allotted to a newly depressed key. The invention also relates to an electronic musical instrument which comprises a plurality of musical tone-generating channels and is so constructed that at least one of the channels can be selected for generation of a new musical tone even while all the channels are generating musical tones.
Some technical terms including "rate" are repeatedly used in this invention so that definitions thereof are given at first as follows:
(a) the word "rate-of-change", or "rate" in brief, means a rate of change per unit time in intensity of the envelope signals, including positive and negative rates;
(b) the word "positive rate" denotes a rate of "increase" per unit time in the intensity of the envelope signals wherein, for example, "greater positive rate" produces a shorter rise time (or sharper leading edge) of fthe envelope signal; and
(c) the word "negative rate" which is a minus value denotes a rate of "decrease" per unit time in the intensity of the envelope signals wherein "greater negative rate" results in quicker attenuation of the envelope signals, thus the adjective "great" or "greater" being used in the sense of "absolute value" of the "negative rate".
It is desirable in the quick-attenuation processing that musical tone attenuation is completed as quickly as possible without causing the so-called click noise. A negative rate at which an intensity or level of envelope signal decreases or decays must be greater for quicker attenuation. On the contrary, the negative rate should be smaller in order not to give rise to the click noise.
A method proposed to meet these two conflicting requirements is disclosed in the Japanese Patent Publication Tokkaisho 62-111290 wherein a predetermined initial negative rate of attenuation is given to a musical tone which is being generated, whatever actual rate-of-change of envelope signal might be found at an instant when the quick-attenuation processing commences. A predetermined greater negative rate for quicker attenuation is imparted to the envelope signal after an actual level thereof has been damped at the predetermined initial negative rate to become lower than a given level.
In known electronic musical instruments which comprise a plurality of musical tone-generating channels, a new musical tone is assigned in general to one of the channels which corresponds to such a musical tone for which attenuation has progressed furthest after key-release, if all of the channels are generating musical tones.
In the known method as mentioned above, the negative rate for attenuation is predetermined and fixed independent upon the actual rate-of-change of envelope signal effective at the instant when the quick-attenuation processing commences. Therefore, it is a common practice that the predetermined negative rate for attenuation of envelope signal is made as lower as possible so as to avoid any sudden change in the rate-of-change whereby any click noise or increase thereof is prevented from taking place. This inevitably leads to a problem such that it takes a considerably long time for the quick-attenuation to be completed.
Further, there is a possibility that the actual negative rate for attenuation of envelope signal which rate is effective at the instant when the quick-attenuation processing commences is greater than the predetermined negative rate. In such a case, the time necessary for quick-attenuation will be prolonged disadvantageously because the greater actual negative rate is reduced to the predetermined smaller negative rate.
It is also noted that the known manner wherein the new musical tone is assigned to the one channel corresponding to the current musical tone for which attenuation has progressed furthest after key-release, does not necessarily mean a proper manner in which the attenuation finishes most quickly without causing a click noise or increase thereof. In other words, there may be another channel which is not selected in such a known manner but is more suited for noiseless quick-attenuation to progress fastest.